a. Field of the Invention
The present invention relates to a method for washing of textiles in hard water and phosphate-free detergent compositions for use therein.
b. Description of the Prior Art
Detergent compositions as developped since the nineteen fourties in general contain phosphates, which have caused environmental pollution. For some time it has been desirable to develop detergent compositions and detergent additives having reduced or no phosphate contents, with a substantially equivalent washing performance and at reasonable price.
It is known that phosphates are incorporated in detergent compositions to bind calcium and magnesium ions present in the water, thus preventing the formation of water insoluble calcium- and magnesium salts of the alkalizing agents and thereby also preserving the surfactant properties of the surface active agents.
Phosphate replacements proposed hitherto are predominantly sodium salts of polyvalent organic acids, such as for example sodium nitrilotriacetate(N.T.A.), sodium citrate and synthetic polyelectrolytes.
However, these are more expensive or less efficient than the customary tripolyphosphate builders(STP) or otherwise unsatisfactory for one reason or another. Thus N.T.A. is more expensive than STP, hygroscopic and has had negative publicity on health factors.
Replacement of STP by sodium citrate would require such an amount, in particular for high temperature washing, that the costs would be unacceptable.
Polyelectrolytes, such as for example sodium acrylates, have a good detergency performance, but they are expensive and have a problematic biodegradability. Many of these organic builders would constitute a new source of water pollution, when used as a sole builder.
Therefore a partial replacement is also encountered; thus zeolites are used in a 1:1 ratio with polyphosphates, thus replacing half of the phosphate contents and reducing their polluting effect only partially.
In the era of the classical fatty acid soaps, preceding the widespread use of phosphates in detergents, alkali metal carbonates were commonly used together with soap in household laundering. The effect of these carbonates was the precipitation of the calcium- and magnesium ions present so as to prevent these ions from binding the fatty acids of the soap. In this way some saving of soap could be achieved, but the calcium- and magnesium carbonates tend to accumulate on the washed fabric, resulting in harshness of the fabric and also deposition on the electrical heating means of washing-machines, causing overheating and early breakdown of the heating means.
Numerous attempts have been made to prepare detergent compositions with sodium carbonate as the main builder, i.e. with complete or substantially complete replacement of the customary phosphates. None of these previous attempts has been completely successful in solving the problems as stated above.
In U.S. Pat. No. 3,996,149 a finely dispersed silicate precipitate is proposed as a nucleant and precipitation aid in order to reduce precipitation on the fabric. However, the precipitation of calciferous deposit is not prevented entirely, causing additional wear of the fabric by the incrustation.
British Patent Specifications Nos. 1,424,406 and 1,437,950 both describe the application of calcite as a nucleant. It not only has the same drawback as the above mentioned dispersed silicate, but in addition the excessively large surface area the fine powder must have to cause the desired effect, makes this method an expensive one.
Cobuilders which have been used together with sodium carbonate as the main builder, have not been particularly successful. Many of them prevent carbonates of bicarbonates from functioning effectively as a precipitating softener in the washing liquor, probably by interference with the growth of crystallites of calcium carbonate, which growth is highly retarded. Utilization of this retarding effect has been proposed in U.S. Pat. Nos. 3,850,852 and 3,925,228 and British Patent Specification No. 2,007,704, wherein citrates, phosphonates and phosphates respectively are proposed as a cobuilder in carbonate-based detergents in limited quantities. Some of the cobuilders mentioned are in their acidic state. However, this is immaterial for practical purposes, as any acidic component will react with the excess of carbonate during processing or storage. Thus the acidic components will be neutralized by the alkakaline components before application in the presence of water. In addition it should be observed that in the latter three patent specifications mentioned above, the surface active agents always comprise fatty acid soaps and alkylbenzene-sulphonates, which are of a type causing a precipitation with the Ca and Mg ions in hard water.
Other systems, wherein initially a cobuilder is dissolved in water and subsequently, after a notable lapse of time, carbonate is released to be dissolved in the water, are described in U.S. Pat. Nos. 3,761,415, 4,210,550 and 4,234,442. The conditions in a solution, thus obtained, are initially acidic and subsequently alkaline at a pH of at least 9, thus still forming a precipitate of carbonate in the end. As stated above, the precipitate of carbonate will cause incrustations and as a result thereof additional wear of the fabric.
In fact all known methods discussed above require the carbonate to precipitate in order to perform a softening action. This softening action is necessary as the use of precipitating active components is implied in all of them. Thus in the latter three publications and in U.S. Pat. No. 4,093,417 the objective is to remove calciferous incrustations of the previous washing cycles by means of predosing or pre-release of an acidic component, or even by an acidic pre-wash. The time lapse between the release of the acidic component and the alkaline component is obtained by coating and granulation techniques, twin sachets and even by addition of insoluble calcium- and magnesium salts, as proposed in German Patent Application No. 2,916,416. It goes without saying that such an addition of calcium- and magnesium salts to a main wash of pH of at least 9 would be very undesirable.
Dutch Patent Application No. 74 05231 describes a detergent composition blended to a water containing product, containing in combination an acidic component and an alkaline component, the ration of these components being such, that the pH at dissolution is in the range of 5 to 8.5. This pH range can be achieved only immediately after the preparation of the detergent composition, which comprises carbonate. It appears that with time the pH at dissolution of such a composition will increase. This is caused by reaction of the acidic components and the alkaline carbonate; even in a dry mixture. Similarly compositions as described in U.S. Pat. No. 4,009,114, comprising citric acid powder and carbonate granules show the neutralizing reaction at least in part before the composition is dissolved in water.
In addition it should be observed that all main washes described are carried out at a pH of at least 9.